1. Field of the Invention
The present invention relates to an optical fiber connector for butt-splicing end surfaces of a pair of optical fibers.
2. Description of the Related Art
An MT type connector in FIG. 7 is an example of a known optical fiber connector. As shown in FIG. 7, the MT type connector for multi-fiber connections includes a first resin plug 22a and a second resin plug 22b to which first optical fibers 21a (not shown) and second optical fibers 21b are fixed, respectively, a pair of guide holes (not shown) formed in the first plugs 22a, a pair of guide pins 23 mounted on the second plug 22b, and a flat metal clamp spring 24. With this configuration, the end surfaces of the optical fibers 21a and 21b are exposed at the splicing side from the end surfaces of the corresponding plugs 22a and 22b and are polished. Then, the first and the second plugs 22a and 22b are coupled by fitting the pair of guide pins 23 into the corresponding guide holes, resulting in tight contact between the polished end surfaces of the optical fibers 21a and the corresponding optical fibers 21b. The clamp spring 24 is used for maintaining the connection between the first optical fibers 21a and the corresponding second optical fibers 21b. 
The MT type connector is capable of high-density mounting and has excellent optical characteristics. However, since it is difficult to form the end surfaces of the optical fibers 21a and 21b to have a spherical shape, a refractive index matching agent is used for filling the spaces between the opposing end surfaces of the optical fibers 21a and 21b so as to reduce the reflection at the spaces. Unfortunately, the refractive index matching agent is not always desirable because the refractive index of the refractive index matching agent is a function of temperature. That is, the refractive index of the refractive index matching agent is highly temperature dependent.
Furthermore, it has been pointed out that attaching and removing the clamp spring 24 used for maintaining the overall structure of the MT type connector as described above is troublesome.
A BF (Bare Fiber) connector is another example of a known optical fiber connector. FIGS. 8A and 8B, respectively, illustrate a state in which the connection is not yet performed and another state in which the connection is complete. The BF connector performs direct butt-splicing between the opposing end surfaces of a pair of optical fibers 31 without a refractive index matching agent.
The BF connector includes a pair of plugs 32 to which the pair of optical fibers 31 are fixed, and an adapter 33 for coupling the opposing plugs 32. Furthermore, each plug 32 includes a holding portion 32a, disposed at the side opposite to the splicing side, for holding the corresponding optical fiber 31 in a cantilever fashion, and a hollow 32b formed therein, having an opening facing toward the mating plug 32, to allow the corresponding optical fiber 31 to buckle. One of the optical fibers 31 fixed in the pair of plugs 32 protrudes by a predetermined distance L1 from the end surface of the opening.
The adapter 33 is constructed so as to connect and fix the pair of plugs 32 inserted from the corresponding ends of the adapter 33, and includes an aligner 34 disposed coaxially therewith. The aligner 34 includes an alignment hole referred to as a micro-hole 35 arranged coaxially therewith so as to receive and align the pair of optical fibers 31 which are fixed in the respective plugs 32 and which are inserted from the corresponding ends thereof. The micro-hole 35 supports the pair of optical fibers 31 inserted from the corresponding ends thereof. The optical fiber 31 protruding by the predetermined distance L1 from the end of the opening of the corresponding plug 32 buckles in the corresponding hollow 32b, resulting in butt-splicing of the end surfaces of the pair of optical fibers 31 in the micro-hole 35.
That is, a pushing force is generated in the buckled optical fiber 31 along the axial direction thereof and pushes the end surface thereof against the end surface of the mating optical fiber 31, thus achieving a close contact between both end surfaces of the pair of optical fibers 31 without a refractive index matching agent. The buckling length L of the buckled optical fiber 31 is defined by the following equation:
L=2xcfx80(EI/P)xc2xd
where P represents a buckling force, and E and I represent the elastic modulus and the second moment of area of the optical fiber 31, respectively.
Further, assuming that an X-axis and a Y-axis lie, respectively, along and perpendicular to the axial direction of the optical fiber 31, a deflection y in the Y-axis direction along x in the X-axis is defined by the following equation:
y=xcex4/2{1xe2x88x92cos(2xcfx80xc3x97/L)}
where xcex4 represents the maximum deflection of the optical fiber 31.
The radius of curvature R of the optical fiber 31 is determined by the following equation:
1/R=yxe2x80x3/(1+yxe2x80x2){fraction (3/2)}
Accordingly, the resulting buckling length L+xcex94L of the optical fiber 31 is defined by the following equation:
L+xcex94L=∫0L{square root over ((1+(yxe2x80x2)2))}dx 
where xcex94L represents a buckling deformation of the optical fiber.
With these equations, the obtained radius of curvature R is about 6 mm when the buckling length L is 7 mm and the buckling deformation xcex94L is 50 xcexcm.
The BF connectors have the following problems. The BF connector has the pair of hollows 32b formed in the respective plugs 32 and holds the pair of optical fibers 31 in a cantilever fashion. This configuration makes it difficult for the optical fibers 31 to be accurately aligned since the buckling directions of the optical fibers 31 are not determined in a uniform manner, and therefore it is difficult for the optical fibers 31 to be inserted into the micro-hole 35 disposed in the adapter 33. A smaller clearance between the outer surface of the optical fibers 31 and the inner surface of the micro-hole 35 makes it more difficult for the optical fibers 31 to be inserted and a larger clearance between the outer surface of the optical fibers 31 and the inner surface of the micro-hole 35 causes displacement of the inserted optical fibers 31 in the micro-hole 35, resulting in an increased insertion loss.
For the BF connector, the recommended amounts of the buckling length L and the buckling deformation xcex94L are 7 mm and 50 xcexcm, respectively, leading to about 6 mm for the radius of curvature R. This radius of curvature R is much smaller than the allowable radius of curvature of typical optical fibers, i.e., about 10 mm. Accordingly, this small radius of curvature may cause the buckled optical fiber 31 to crack. To avoid this, it is necessary to coat the optical fibers 31 with carbon. However, this kind of treatment involves a substantial increase in cost.
In order to overcome the problems described above, preferred embodiments of the present invention provide an optical fiber connector for reliably and accurately aligning optical fibers and allowing the optical fibers to surely and easily have a radius of curvature that is substantially equal to or larger than the allowable radius of curvature.
According to a preferred embodiment of the present invention, an optical fiber connector includes a first holder for holding a first connection end of a first optical fiber and a second holder for holding a second connection end of a second optical fiber. The first and the second holders include a first holder portion and a second holder portion disposed therein, respectively. The first and the second holder portions include a first holding groove and a second holding groove disposed therein, respectively. The first holding groove holds the top half of the first connection end and allows the bottom half thereof to be exposed, and the second holding groove holds the bottom half of the second connection end and allows the top half thereof to be exposed, where the top half and the bottom half are defined with respect to the central axis of any of the first and the second optical fibers. The first and the second holding grooves include a pair of first inclined planes and a pair of second inclined planes, respectively, disposed therein, where the first inclined planes align the top half of the first connection end and the second inclined planes align the bottom half of the second connection end. With this configuration, a first fiber end surface of the first optical fiber recedes from a first holder end surface of the first holder portion and a second fiber end surface of the second optical fiber recedes from a second holder end surface of the second holder portion, the first holding groove and the second holding groove oppose each other sandwiching at least one of the first and the second connection ends therebetween, and the receded portion of the first holding groove aligns the second optical fiber. Thus, the first fiber end surface of the first optical fiber and the second fiber end surface of the second optical fiber are butt-spliced by coupling the first holder and the second holder together.
In the optical fiber connector according to the preferred embodiment of the present invention described in the preceding paragraph, each of the pair of holders preferably has the corresponding holding groove, e.g., a substantially V-shaped groove, disposed in the holding portion of the holder. The holding groove has the pair of inclined planes for aligning and holding either one of the upper half and the bottom half of the corresponding optical fiber with respect to the central axis of the optical fiber. When the pair of holders are coupled to each other, the first holding groove of the first holder portion and the second holding groove of the second holder portion oppose each other sandwiching at least one of the pair of optical fibers therebetween. Accordingly, the second holding groove is automatically aligned while tracking the first optical fiber aligned and held by the first holding groove. Thus, the posture of the second optical fiber aligned and held by the second holding groove is adjusted, achieving highly accurate alignment of the pair of optical fibers, and also leading to a reduced insertion loss while making the holders simple in their construction.
In the optical fiber connector according to preferred embodiments of the present invention, the first receding distance from the first holder end surface to the first fiber end surface is preferably different from the second receding distance from the second holder end surface to the second fiber end surface.
In the optical fiber connector, the first receding distance from the first holder end surface to the first fiber end surface is preferably different from the second receding distance from the second holder end surface to the second fiber end surface. This results in causing a time difference between the time when the holding groove is aligned by the second optical fiber and the time when the first optical fiber is aligned by the second holding groove. That is to say, the first holding groove aligning the first optical fiber slides on the second optical fiber aligned by the second holding groove while tracking the second optical fiber first, and thus allowing the second optical fiber to align the first holding groove, then allowing the second holding groove to align the first optical fiber, surely resulting in a highly accurate alignment of two optical fibers.
In the optical fiber connector according to preferred embodiments of present invention, at least one of the first holder and the second holder may have a guide for allowing the corresponding optical fiber to have a radius of curvature that is substantially equal to or larger than the allowable radius when the corresponding optical fiber is buckled by abutting against the mating optical fiber.
In the optical fiber connector according to preferred embodiments of the present invention, at least one of the first holder and the second holder has a guide for allowing the corresponding optical fiber to have a radius of curvature that is substantially equal to or larger than the allowable radius when the corresponding optical fiber is buckled by abutting against the mating optical fiber, thus preventing the corresponding optical fiber from having a radius smaller than the allowable radius. Accordingly, this guide prevents the buckled optical fiber from cracking and makes it unnecessary to coat the optical fiber for protecting the optical fiber against cracking. Furthermore, although a multi-fiber connector may have variations in the lengths of optical fibers therein, this configuration automatically accommodates the variations in the lengths of the optical fibers.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.